1. Field of the Invention
The present invention relates to a method and arrangement for Radio-Frequency (RF) high power generation comprising at least one power combiner having RF inputs and at least one RF output, and at least two power amplifier modules, which are respectively electrically connected by at least one transmission line to an input of the at least one power combiner.
2. Description of the Related Art
Radio-Frequency Radio-Frequency (RF) and/or microwave power is produced with appropriate generators. RF power generators for high power applications are based on tubes, such as klystrons, inductive output tubes or magnetrons. Alternatively, solid state technology is used for RF power generators, particularly transistor technology. With solid state RF power generators, a reliable RF power production with small dimensions and high efficiency is possible. One disadvantage of transistor technology is a low RF power output per transistor chip, in the range of up to 1.5 kW power output at 500 MHz frequency. For comparison, with klystrons as an example for tube technology, up to some Megawatt RF power output is possible.
To generate high amounts of power with, for example, transistor based RF generators, an aggregation of RF generators is necessary. An aggregation of transistors in a single power amplifier (PA) based, for example, on push- pull or a balanced kind of topology, can increase the complexity of the system and increases the risk of failure. If single transistors fail, the entire device must be exchanged. An alternative way to generate high levels of power is to use a number of power amplifier modules with a common, particularly single power combiner.
In a modular arrangement, RF power from power amplifier modules, connected via transmission lines to the common power combiner, is aggregated in the power combiner to a high RF power. For example, coaxial cables and/or strip-lines are used as transmission lines. Due to different length and properties, each of the transmission lines introduces an individual power loss and signal phase shift to the arrangement. This leads to the appearance of back reflected power from the power combiner input, which can be unequally divided between power amplifiers, i.e., RF modules. It causes additional power losses, reduces the overall output RF power and can lead to overheating of amplifiers.
To reduce or prevent losses, each RF module must be configured separately to generate an individual signal with a certain amplitude and a certain phase, in order to provide equal signals to the power combiner. US20130170512A1 and US20130051416A1, for example, disclose the adjustment of RF modules that is performed manually. Here, all RF modules are fed in-phase by a single pre-amplified oscillator, and amplitude as well as phase of each RF module connected to the power combiner is manually adjusted, using selectively variable impedance circuits connected to a respective input of each RF module. The disclosed conventional method can only be applied, if the length of the transmission line is permanent. Changes in length thus necessitates a new adjustment. After the system is once assembled, it can hardly be adjusted. Deviations of electronic components, such as by aging, cannot be compensated for and increase losses.
Alternatively, amplitudes and phases of RF module signals can be continuously monitored and adjusted during amplifier operation. Additional devices, such as numerous directional couplers, are necessary and have to be installed in each RF module output branch, thereby increasing costs and complexity.